1. Field of the Invention
This invention relates to a position pointer suitable for use for detection of writing pressure, a variable capacitor for detecting the writing pressure, and an inputting apparatus which includes the position pointer.
2. Description of the Related Art
In recent years, inputting apparatuses have been used as an inputting device for computing devices, such as personal computers and so forth. A typical inputting apparatus includes a position pointer formed, for example, like a pen, and a position detection apparatus having an input face which receives a pointing operation or inputting of characters, figures, and so forth thereto using the position pointer.
A variable capacitor, disclosed, for example, in Japanese Patent Laid-Open No. H4-96212 (hereinafter referred to as Patent Document 1), is used in a writing pressure detection section of the position pointer. The variable capacitor disclosed in Patent Document 1 includes a first electrode attached to a first face of a dielectric member and a second flexible electrode disposed on a second face side of the dielectric member. The variable capacitor further includes means for spacing the second electrode away from the second face of the dielectric member at a small distance, and means for applying relative pressure or displacement between the second electrode and the dielectric member.
FIGS. 26A and 26B show a particular configuration of the conventional variable capacitor. More particularly, FIG. 26A shows the variable capacitor in an initial state, and FIG. 26B shows the variable capacitor in a state when pressure is applied thereto.
Referring to FIGS. 26A and 26B, the variable capacitor 200 includes a dielectric member 201 substantially shaped as a disk, a first electrode 202 attached to the first face 201a of the dielectric member 201, and a second electrode 203. The second electrode 203 has flexibility and is disposed on the second face 201b side of the dielectric member 201 with a ring-shaped spacer 204 interposed therebetween. Meanwhile, a bar-like rod 210 is provided on the opposite side of the second electrode 203 opposite to the dielectric member 201 with an elastic member 205 interposed therebetween.
A first terminal 206 is provided on the first face side of the first electrode 202. The first terminal 206 has a disk-shaped flange portion 206a and a lead portion 206b extending from a substantially central portion of a face of the flange portion 206a. When writing pressure is applied to the flange portion 206a through the rod 210, the flange portion 206a contacts the first face of the first electrode 202 and electrically connects to the first electrode 202.
A second terminal 207 is provided at an end portion of the second electrode 203. Similarly to the first terminal 206, the second terminal 207 has, a disk-shaped flange portion 207a and a lead portion 207b extending from a substantially central portion of one face of the flange portion 207a. When writing pressure is applied through the rod 210, the flange portion 207a is brought into contact with an end portion of the face of the second electrode 203 and electrically connects to the second electrode 203.
In the variable capacitor 200, when no pressure or displacement is applied to the rod 210, that is, in an initial state, a small distance is formed between the second face 201b of the dielectric member 201 and the second electrode 203 by the spacer 204, as seen in FIG. 26A. If pressure is applied to the rod 210, the elastic member 205 and the second electrode 203 are pressed and elastically deformed by the rod 210, as seen in FIG. 26B. By the elastic deformation, the second electrode 203 is brought into contact with the second face 201b of the dielectric member 201. Then, if higher pressure is applied to the second electrode 203 through the rod 210, the contact area between the second electrode 203 and the second face 201b of the dielectric member 201 increases, and the capacitance value between the first and second terminals 206 and 207 also increases. The variation in capacitance value between the first and second terminals 206 and 207 is detected to determine the writing pressure applied to the rod 210.